import LRU from './LRU';

var globalImageCache = new LRU(50);

/**
 * @param {string|HTMLImageElement|HTMLCanvasElement|Canvas} newImageOrSrc
 * @return {HTMLImageElement|HTMLCanvasElement|Canvas} image
 */
export function findExistImage(newImageOrSrc) {
  if (typeof newImageOrSrc === 'string') {
    var cachedImgObj = globalImageCache.get(newImageOrSrc);
    return cachedImgObj && cachedImgObj.image;
  } else {
    return newImageOrSrc;
  }
}

/**
 * Caution: User should cache loaded images, but not just count on LRU.
 * Consider if required images more than LRU size, will dead loop occur?
 *
 * @param {string|HTMLImageElement|HTMLCanvasElement|Canvas} newImageOrSrc
 * @param {HTMLImageElement|HTMLCanvasElement|Canvas} image Existent image.
 * @param {Element} [hostEl] For calling `dirty`.
 * @param {Function} [cb] params: (image, cbPayload)
 * @param {Object} [cbPayload] Payload on cb calling.
 * @return {HTMLImageElement|HTMLCanvasElement|Canvas} image
 */
export function createOrUpdateImage(newImageOrSrc, image, hostEl, cb, cbPayload) {
  if (!newImageOrSrc) {
    return image;
  } else if (typeof newImageOrSrc === 'string') {
    // Image should not be loaded repeatly.
    if ((image && image.__qrImageSrc === newImageOrSrc) || !hostEl) {
      return image;
    }

    // Only when there is no existent image or existent image src
    // is different, this method is responsible for load.
    var cachedImgObj = globalImageCache.get(newImageOrSrc);

    var pendingWrap = { hostEl: hostEl, cb: cb, cbPayload: cbPayload };

    if (cachedImgObj) {
      image = cachedImgObj.image;
      !isImageReady(image) && cachedImgObj.pending.push(pendingWrap);
    } else {
      image = new Image();
      image.onload = image.onerror = imageOnLoad;

      globalImageCache.put(
        newImageOrSrc,
        (image.__cachedImgObj = {
          image: image,
          pending: [pendingWrap],
        }),
      );

      image.src = image.__qrImageSrc = newImageOrSrc;
    }

    return image;
  }
  // newImageOrSrc is an HTMLImageElement or HTMLCanvasElement or Canvas
  else {
    return newImageOrSrc;
  }
}

function imageOnLoad() {
  var cachedImgObj = this.__cachedImgObj;
  this.onload = this.onerror = this.__cachedImgObj = null;

  for (var i = 0; i < cachedImgObj.pending.length; i++) {
    var pendingWrap = cachedImgObj.pending[i];
    var cb = pendingWrap.cb;
    cb && cb(this, pendingWrap.cbPayload);
    pendingWrap.hostEl.dirty();
  }
  cachedImgObj.pending.length = 0;
}

export function isImageReady(image) {
  return image && image.width && image.height;
}
